The present invention relates in general to cathode ray tubes, and more particularly to methods of making an electron gun having a single cathode, a control grid, a first anode, a focusing anode, and an accelerating anode, for producing an electron beam to be scanned repetitively along a phosphor screen, such as color-producing phosphor screens, to produce image displays on the faceplate of a cathode ray tube.
Most frequently, cathode ray tubes of the type used to produce the color image for multi-color displays for television receivers, computer readout displays, and the like, particularly those commonly referred to as color picture tubes, have customarily been of the shadow mask type having openings precisely positioned for passage of electron beams therethrough onto color-producing phosphor dots on the faceplate, and have customarily employed an electron gun assembly forming a battery or array of three electron guns for producing three electron beams which approach the shadow mask along different angles of divergence to selectively direct them onto phosphor dots of selected colors. Each electron gun customarily includes its own cathode and heating filament, its own control grid, first anode, focusing anode and accelerating anode for controlling the electron beam produced by the electrons emitted by the associated cathode.
More recently, cathode ray tubes for color television image production or other multi-color readout display have been devised wherein a single electron gun is provided for producing a single electron beam or three electron beams which are scanned over the phosphor screen area of the faceplate of the cathode ray tube in selected fashion, without the use of a shadow mask, thereby eliminating the significant cost and complexity of shadow mask type cathode ray tube construction as well as reducing the cost of the electron gun assembly compared to three gun cathode ray tubes. Some of these prior single gun cathode ray tubes have involved scanning one or a plurality of electron beams along the longitudinal axis of substantially horizontal strips of color phosphor making up the phosphor screen, while others have involved the scanning of a single beam substantially horizontally across the screen area to intercept vertically elongated phosphor strips vertically spanning the screen area and arranged in selected sequence to be successively intercepted by the electron beam.
My earlier U.S. Pat. Nos. 3,194,641 and 3,771,002 disclose a cathode ray tube and electron gun structure wherein a single electron gun produces one or a plurality of beams to be scanned relative to strips of color phosphor material to intercept the phosphors in selected fashion and produce color images. The electron gun structure of those patents involves, in addition to the cathode, focusing anode and accelerating anode elements, the provision of a control grid and first anode, sometimes also referred to as G-1 and G-2 electrodes, fixed to the same supporting frame as the other elements and formed of a ceramic substrate or panel, there shown to be of oval profile, with each of the substrates having one or more precisely sized and located beam-forming apertures therethrough and one of the faces of each of the substrates being coated with a thin, precisely formed layer of metal which also lines the cylindrical surfaces of the apertures, and which has suitable connections to conductive leads to the biasing voltage source for the electron gun elements.
It will be appreciated that a very high degree of alignment accuracy and precision is required with respect to the supporting arrangement for the various elements of the electron gun and for the relative location of the beam-forming apertures in the control grid and first anode to achieve proper directivity configuration and size of the electron beam or beams. As higher resolution is required in cathode ray tubes, the size of the phosphor strips or other phosphor elements making up the image screen is made smaller, requiring better shaping and landing accuracy of the electron beam and thus giving rise to a lower tolerance of errors caused by poor alignment of the electron gun elements. Maintenance of proper beam-forming hole size and location in the metal layers on the subtrates for the control grid and first anode with the requisite accuracy becomes more and more difficult if they are to be formed by conventional hole-forming processes, especially as the requirement for beam sizes of smaller and smaller diameter becomes greater. Also poor alignment may arise at various stages of the assembly process for electron guns, as the electron gun elements are customarily mounted on support rods, commonly made of an electrical insulating material such as glass, with the various elements of the electron gun assembled to the elongated glass support rods by radially extending mounting wires embedded in the glass rods and fastened to the perimeters of the electron gun elements or to metallic shields surrounding and affixed to such elements. All of these factors give rise to considerable difficulty and expense in attempting to achieve satisfactory uniformity in mass production of such electron guns and have stimulated a desire for improved methods of manufacture of electron guns of this type.
An object of the present invention, therefore, is the provision of a novel method of manufacture of an electron gun for producing a single electron beam or plural electron beams for cathode ray tubes and the like, wherein apertures for the metallic conductive layer on the substrate of the control grid and first anode elements of the electron gun are precisely formed after assembly of these elements on the electron gun supporting framework by positioning such subassembly on a suitable bench assembly, preferably vibration-free, provided with means for producing a laser beam of appropriate diameter and means for directing the laser beam onto the metallic layers of the control grid and first anode elements to produce apertures of the precise desired size, shape and location, and thereafter assembling the remaining electron gun elements such as the filament and other electrodes on the supporting framework.
Another object of the present invention is the provision of a novel method of forming an electron gun for producing a single electron beam for cathode ray tubes and the like in which the electron gun includes a cathode, focusing and accelerating anodes, and a control grid and first anode comprising a pair of substrate elements each having a thin layer of metal on the surface thereof and a preformed aperture in the substrate material, wherein the substrate elements and associated metal layers are assembled on an electron gun supporting framework before positioning of the cathode element thereon and such subassembly is placed on a suitable bench assembly provided with a laser light beam source producing a laser beam diameter no larger than the minimum transverse dimension of the electron beam to be produced, and positioning such subassembly relative to the laser beam source so that the laser beam passes through the preformed apertures in the substrate elements and onto the metallic layers thereby forming the apertures of appropriate shape, size and position in the metallic layers of the substrate elements, and thereafter assembling the remaining elements to the supporting framework to complete the electron gun.
Another object of the present invention is the provision of a novel method of producing an electron gun as described in the immediately preceding paragraph, wherein electron beam-forming apertures of oval or elongated slot shape configuration are provided in the metallic layers on the substrates by subjecting the laser beam and/or the substrate elements to controlled relative transverse movement with respect to the laser beam axis to produce non-round transversely elongated apertures of appropriate size and shape in the metallic layers associated with the substrate.
It will be evident that the present invention may also be used in fabricating electron guns intended for use in devices other than cathode ray tubes. For example, television camera tubes such as the image orthicon and vidicon tubes employ electron guns, the production of which will also benefit by applying the novel method disclosed herein.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.